Field of the Invention
The present invention relates to a method for producing a polyphenylene ether.
Description of the Related Art
A polyphenylene ether (hereinafter, sometimes simply referred to as “PPE”), and/or a resin composition including PPE and other thermoplastic resin (hereinafter, sometimes referred to as “modified PPE resin”) have characteristics such as excellent electrical insulation, heat resistance, hydrolysis resistance and flame retardance, and enable to produce a product having a desired shape and various components by a molding method such as a melt injection molding method or a melt extrusion molding method, and therefore are widely used in materials for products and components in the electric and electronic fields, the automobile field and other various industrial material fields.
As a method for producing PPE, a method has been conventionally known which includes subjecting a phenol compound to oxidative polymerization in a good solvent for PPE, such as toluene, xylene or ethylbenzene, in the presence of a polymerization catalyst including a metal compound and an amine compound.
As a method for isolating PPE from the polyphenylene ether solution (which means a solution in which PPE is dissolved in the good solvent, and is also referred to as “PPE solution”) obtained by the above method, a method has been known which includes adding a poor solvent for PPE, such as methanol, to the PPE solution to thereby precipitate PPE as a particle.
A method has also been proposed which includes performing, as the previous step of the precipitation, a step of heating the PPE solution to evaporate the good solvent for concentration of the PPE solution.
Patent Literature 1 describes a method for removing a part of a solvent for a PPE solution after oxidative polymerization to produce a concentrated liquid having a cloud point (Tcloud).
Patent Literature 1 describes the following: the concentrated liquid can be produced to thereby inhibit production of a fine PPE particle.
Patent Literature 2 describes a method including performing polymerization, with the concentration of a phenol being set to be about 5 to about 15% by mass based on the total amount of the phenol and a solvent, for the purpose of producing a poly(arylene ether) having a high intrinsic viscosity, and preliminarily concentrating the poly(arylene ether) prior to isolation by segmentation.
Patent Literature 2 describes the following: the method can be applied to thereby produce the poly(arylene ether) having a high intrinsic viscosity.
Patent Literature 3 mainly describes a method for removing a polymerization catalyst, and describes a method for concentrating a mixture of a polymer and a solvent, which can be arbitrarily performed.
Patent Literature 3 describes a method for enhancing the removal efficiency of the catalyst to decrease the remaining catalyst, but the method is not made by concentration of the mixture of a polymer and a solvent.